The behavioral and physiological effects of electrical brain stimulation have been studied in a variety of contexts. Depending upon locus of stimulation, parameters of the stimulus, and the environmental situation in which the organism is placed, the stimulation may have several consequences, including specific motivational effects, changes in level of arousal, and reinforcing effects. Each stimulation probably also has sensory consequences. In the past, these have been studied by obtaining verbal reports from patients, and by requiring nonhuman subjects to use the stimulation as discriminative or conditioned stimuli. The present proposal outlines experiments which provide an assessment of the sensory aspects of such electrical stimulation. Laboratory animals (rats) will be trained as subjects in a signal detection situation, with the signals being very weak versions of the stimuli typically employed to demonstrate positive reinforcement effects. From this procedure, estimates can be obtained of the sensitivity of the animal to the electrical stimulus when parameters of the stimulus are varied, when specific lesions are placed in areas implicated in the reinforcement phenomenon, and when motivational states are manipulated. The results are expected to contribute to the general understanding of the sensory aspects of motivation and reinforcement, especially as these phenomena are related to electrical stimulation of the brain.